The process of manufacturing photographic paper or film consists of coating several layers on top of either a laminated paper or a transparent polymer support like triacetate cellulose film. These layers comprise emulsion layers which contain the photosensitive silver halide crystals as an essential component, and intermediate layers which do not contain these photosensitive components.
The process of silver halide grain formation is controlled by the use of dispersing agents, usually referred to as peptisers. A nucleation peptiser is used during the precipitation of the silver halide grains to avoid uncontrolled coalescence. A growth peptiser is used during the growth process as dispersion stabiliser of the silver halide crystals, which functionality is also used between the different growth steps as well as after the end of the growth process when the crystals should remain stabilised under storage conditions. It is well known that tabular grains with high aspect ratio have several photographic advantages like increased sharpness, improved speed granularity relationships, more rapid developability and higher silver covering power (Research Disclosure Vol. 225 January 1983, Item 22534; EP-A-0.610.796). It has also been desired to produce tabular grains not only with high aspect ratio but also with a narrow grain size distribution, otherwise expressed as a desire for mono- or homodispersity.
Polypeptides are often used as peptisers in photographic manufacturing processes. Suitable polypeptides are collagen-like proteins such as gelatin in its numerous forms. Gelatin used in commercial processes has commonly been derived from animal sources such as animal bone and hide. Disadvantages of this material are the presence of impurities like non-collagenic protein, mucopolysaccharides, polynucleic acid and lipids and the fact that the nature of the composition is not clearly defined and thus not reproducible. In addition it is also unclear which components actually are required for optimal activity. The reproducibility of the photographic manufacturing process is questionable due to the lack of consistency of the gelatin composition used at various stages of the photographic manufacturing process.
U.S. Pat. Nos. 5,580,712, 5,670,616 and 5,710,252 are concerned with modified collagen-like polypeptides, their preparation and their application for photographic purposes. These patents disclose that collagen-like peptisers with silver binding strengths below 50 mV can lead to a high degree of thin tabular grain and illustrate this for a number of synthetically produced polypeptides with a length of 25 amino acids. These patents also disclose a polypeptide with a collagen-like structure which was produced using recombinant technology. The recombinant polypeptide is a synthetic polypeptide having a block copolymer structure consisting of 4 different amino acids (Gly, Pro, Glu and Gln), or a 25-mer peptide starting with Gly-Pro-Xaa1-Gly-Leu-Xaa2-Gly-Pro-Arg- (SEQ ID NO:1), wherein Xaa1 and Xaa2 are Met, Ile, His, Lys, Asn, Tyr or Gln.
EP applications 0926543 and 1014176 disclose the use of recombinant collagen-like biopolymers to produce silver halide emulsions wherein the tabular grains account for more than 75% of the total grain projected area. These collagen-like materials can be produced with high, economically feasible expression rates, without being susceptible to protease attack, and such recombinant material can be used in the preparation of photographic silver halide emulsion with improved photographic properties.
WO 9210567 discloses a helical structure wherein each ‘screw’ in the helix has a polar side and an apolar side such that the amphiphilic protein is folded flat covering the whole interface. JP-A 9-278793 discloses a similar structure in which hydrophobic and hydrophilic regions are located at opposite sides of the helix-structure. These patent applications are not concerned with for photographic applications, while the disclosed proteins are also not suitable for these photographic applications, because the interface surface would be covered to a large extent.